diff --git a/h5bp/directive-only/no-transform.conf b/h5bp/directive-only/no-transform.conf
index 1bb5fc1..eda5464 100644
--- a/h5bp/directive-only/no-transform.conf
+++ b/h5bp/directive-only/no-transform.conf
@@ -1,2 +1,11 @@
 # Prevent mobile network providers from modifying your site
+#
+# (!) If you are using `ngx_pagespeed`, please note that setting
+# the `Cache-Control: no-transform` response header will prevent
+# `PageSpeed` from rewriting `HTML` files, and, if
+# `pagespeed DisableRewriteOnNoTransform off` is not used, also
+# from rewriting other resources.
+#
+# https://developers.google.com/speed/pagespeed/module/configuration#notransform
+
 add_header "Cache-Control" "no-transform";